1. Field of the Invention
The present invention relates to a method and device for a touch sensor, and more particularly, to a method and device for a touch sensor with touches that are close to each other.
2. Description of the Prior Art
A traditional mutual capacitive sensor includes an insulating surface layer, a first conductive layer, a dielectric layer, and a second conductive layer, wherein each of the first and second conductive layers have a plurality of first conductive strips and second conductive strips that are made up by a plurality of conductive pads and connection wires connecting these conductive pads in series.
In mutual capacitive sensing, one of the first and second conductive layers is driven, while the other one is sensed. For example, a driving signal is sequentially provided to each of the first conductive strips, and corresponding to each first conducting strip being driven by the driving signal, signals from all of the second conducting strips are sensed, which represent capacitive coupling signals at intersections between the driven first conducting strip and the respective second conducting strips. As such, capacitive coupling signals representing intersections between all of the first and second conducting strips can be obtained, forming an image of capacitive values.
As such, a capacitive-value image before any touch is obtained as a basis, and this basis is compared with capacitive-value images detected subsequently to determine if there is a touch or proximity of an external object, and further determine the location of the touch or proximity.
The portion corresponding to a touch or proximity of an external object in the capacitive-value image is called “touch related sensing information”. When two external objects are too close to each other, the touch related sensing information corresponding to different external objects may partially overlap. If the locations are determined directly using the overlapped portion, there will be large errors in the locations of these two external objects, and the determined locations will be closer than the actual locations, as if they are mutually attracted.
Referring to FIGS. 1A, 1B and 1C, schematic diagrams illustrating how to calculate the locations of two neighboring fingers in the prior art are shown. FIG. 1A shows a one-dimensional (1D) sensing information obtained based on all of the second conducting strips as described earlier. When a first finger approaches or touches a first conducting strip that is currently being driven, it will cause a corresponding profile of values S1 to appear in the 1D sensing information. Each value corresponds to a location. Therefore, based on the values and the locations, the centroid location P1 of the first finger can be calculated to be at the location of 3 ((1×2+2×5+3×7+4×5+5×1)/(2+5+7+5+2)=3). Similarly, FIG. 1B shows a corresponding profile of values S2 for a second finger. If there are no overlap between the profile values of the first finger and the second finger, then the centroid location P2 of the second finger can be calculated to be at the location of 7 ((5×1+6×6+7×9+8×6+9×1)/(1+6+9+6+1)=7).
However, as shown in FIG. 1C, if profile values S12 of overlapping portion of the first and the second fingers are used directly for calculating the centroid locations, then there will be error. The resulting error locations of the first and the second fingers Pe1 and Pe2 are 3.09 ((1×2+2×5+3×7+4×5+5×3)/(2+5+7+5+3)=3.09) and 6.84 ((5×3+6×6+7×9+8×6+9×1)/(3+6+9+6+1)=6.84), respectively.
For systems that have little tolerance on errors, the above location errors may exceed the error tolerance limit. For example, the error tolerance limit of a system is 1 mm, and the corresponding location width between the second conducting strips is 7 mm. The error location of the second finger is offset from the original centroid location by 0.16 location width, i.e. about 1.02 mm, which exceeds the error tolerance limit of the system.
From the above it is clear that prior art still has shortcomings. In order to solve these problems, efforts have long been made in vain, while ordinary products and methods offering no appropriate structures and methods. Thus, there is a need in the industry for a novel technique that solves these problems.